Dear Customer: April 10, Attached is the monthly water supply outlook and projected operations for Yellowtail Dam and Powerplant. If you have any questions or concerns, please feel free to call me at 406-247-7334 or Stephanie Micek 406-247-7320. Clayton R. Jordan Reservoir and River Operations U. S. Department of the Interior Bureau of Reclamation Montana Area Office River and Reservoir Operations
YELLOWTAIL RESERVOIR OPERATIONS Water Supply Forecasts and Reservoir Operations April 1, Present Elevations & Storages: Elevation Storage Percent of Percent (feet) (acre-feet) Average Full Boysen 4715.37 571,409 108 77 Buffalo Bill 5363.58 423,449 102 * 65 Bighorn Lake 3611.57 773,223 101 76 Inflows (1,000 s of Acre-Feet): Water Year Inflow Percent of Average October 277.8 (3 rd highest or record) 174 November 229.8 (3 rd highest of record) 193 December 177.4 174 January 177.3 173 February 158.9 147 March 308.2 (highest of record) 211 Water Year 2017 Inflow Percent of Average March 306.7 (highest of record) 216 April 603.4 (highest of record) 411 May 813.0 (highest of record) 296 June 920.4 (3 rd highest of record) 217 July 616.3 (6 th highest of record) 249 August 216.4 147 September 219.0 135 April-July 2,953.1 (highest of record) 270 Gains between Boysen and Buffalo Bill to Yellowtail (1,000 s of Acre-Feet): Water Year Gains Percent of Average October 64.2 94 November 72.5 126 December 54.7 145 January 69.0 171 February 54.0 105 March 131.8 (3 rd highest of record) 183 Water Year 2017 Gains Percent of Average March 98.0 137 April 136.5 (highest of record) 411 May 143.7 272 June 162.1 184 July -96.8 (avg. -62.1) - August -37.1 (avg. -51.9) - September 31.6 319 April 1 Runoff Forecast (April through July Inflows - 1,000 s of Acre-Feet): Inflow Percent of Average April through July 1,864.8 160 Average based on past 30 years *This does not reflect the 30 year average because in 1992 the capacity of the reservoir was increased to approximately 646,565 acre-feet as a result of raising the dam. The average used here reflects data from 1993 through 2017.
BASIN Data Site Name SNOW and PRECIPITATION UPDATE Based on Mountain Data from NRCS SNOTEL Sites As of April 1, Elev. feet UPPER YELLOWSTONE RIVER BASIN Snow Water Equivalent % Current Total Precipitation % Current Beartooth Lake 9360 37.1 21.0 177 32.5 18.9 172 Box Canyon 6670 16.0 8.6 186 16.2 12.1 134 Brackett Creek 7320 30.3 19.0 159 31.8 24.1 132 Burnt Mtn 5880 6.8 4.4 155 13.5 12.1 112 Canyon 7870 16.6 12.3 135 19.0 15.5 123 Cole Creek 7850 13.6 13.5 101 10.8 12.0 90 East Boulder Mine 6335 7.9 -M * 15.1 -M * Evening Star 9200 39.3 23.9 164 40.9 26.1 157 Fisher Creek 9100 50.4 30.1 167 44.5 30.4 146 Monument Peak 8850 31.1 18.8 165 29.0 20.6 141 Northeast Entrance 7350 13.8 9.6 144 17.6 11.7 150 Parker Peak 9400 32.3 18.8 172 28.0 16.9 166 Placer Basin 8830 25.8 16.6 155 26.6 18.0 148 Porcupine 6500 11.4 5.9 193 16.8 11.4 147 Sacajawea 6550 19.4 14.8 131 27.7 21.2 131 Shower Falls 8100 27.6 20.7 133 27.1 22.1 123 S Fork Shields 8100 22.6 15.3 148 28.1 19.2 146 Sylvan Lake 8420 24.3 19.2 127 25.6 21.3 120 Sylvan Road 7120 13.4 11.1 121 20.2 16.1 125 Thumb Divide 7980 18.9 14.9 127 19.1 17.8 107 Two Ocean Plateau 9240 36.0 25.6 141 28.2 26.2 108 White Mill 8700 39.3 21.6 182 30.4 22.7 134 Wolverine 7650 20.4 9.1 224 19.9 11.7 170 Younts Peak 8350 -M 14.1 * -M 15.2 * Basin Index (%) 154 136 WIND RIVER BASIN (WYOMING) Burroughs Creek 8750 15.7 -M * 17.4 -M * Castle Creek 8400 8.2 -M * 9.5 -M * Cold Springs 9630 9.5 7.1 134 9.7 9.5 102 Deer Park 9700 12.3 14.7 84 15.2 18.6 82 Hobbs Park 10100 16.9 13.4 126 14.4 12.5 115 Kirwin 9550 19.1 9.4 203 17.2 11.0 156 Little Warm 9370 15.4 10.2 151 15.9 12.3 129 Owl Creek 8975 4.3 5.5 78 6.0 5.7 105 South Pass 9040 11.9 14.9 80 8.8 16.6 53 St. Lawrence Alt 8620 3.0 6.8 44 8.3 8.5 98 Togwotee Pass 9580 30.8 21.6 143 31.1 23.3 133 Townsend Creek 8700 7.1 9.0 79 9.1 11.3 81 Younts Peak 8350 -M 14.1 * -M 15.2 * Basin Index (%) 116 105 SHOSHONE RIVER BASIN (WYOMING) Blackwater 9780 32.8 22.1 148 30.6 19.7 155 Evening Star 9200 39.3 23.9 164 40.9 26.1 157 Marquette 8760 5.7 -M * 9.5 -M * Sylvan Lake 8420 24.3 19.2 127 25.6 21.3 120 Sylvan Road 7120 13.4 11.1 121 20.2 16.1 125 Younts Peak 8350 -M 14.1 * -M 15.2 * Basin Index (%) 144 141
BASIN Data Site Name SNOW and PRECIPITATION UPDATE Based on Mountain Data from NRCS SNOTEL Sites As of April 1, Elev. Current Snow Water Equivalent % Current Total Precipitation % BIGHORN BASIN ABOVE YELLOWTAIL DAM Bald Mtn. 9380 20.5 18.6 110 14.6 16.3 90 Bear Trap Meadow 8200 10.4 5.1 204 10.9 8.1 135 Blackwater 9780 32.8 22.1 148 30.6 19.7 155 Bone Springs Div 9350 18.7 15.9 118 14.4 14.8 97 Burroughs Creek 8750 15.7 -M * 17.4 -M * Castle Creek 8400 8.2 -M * 9.5 -M * Cold Springs 9630 9.5 7.1 134 9.7 9.5 102 Deer Park 9700 12.3 14.7 84 15.2 18.6 82 Evening Star 9200 39.3 23.9 164 40.9 26.1 157 Grave Springs 8550 7.6 8.9 85 5.5 10.0 55 Kirwin 9550 19.1 9.4 203 17.2 11.0 156 Little Warm 9370 15.4 10.2 151 15.9 12.3 129 Marquette 8760 5.7 -M * 9.5 -M * Middle Powder 7760 9.6 11.4 84 6.3 11.1 57 Owl Creek 8975 4.3 5.5 78 6.0 5.7 105 Powder River Pass 9480 16.2 10.0 162 15.4 12.0 128 Shell Creek 9580 20.7 14.5 143 15.7 13.2 119 South Pass 9040 11.9 14.9 80 8.8 16.6 53 St. Lawrence Alt 8620 3.0 6.8 44 8.3 8.5 98 Sylvan Lake 8420 24.3 19.2 127 25.6 21.3 120 Sylvan Road 7120 13.4 11.1 121 20.2 16.1 125 Timber Creek 7950 3.4 4.8 71 2.5 7.0 36 Togwotee Pass 9580 30.8 21.6 143 31.1 23.3 133 Townsend Creek 8700 7.1 9.0 79 9.1 11.3 81 Younts Peak 8350 -M 14.1 * -M 15.2 * Basin Index (%) 125 111 M = Missing data * = Data may not provide a valid measure of conditions. Units = inches for the Current and Normal Snow Water Equivalent and Total Precipitation values
22 Snowpack above Bighorn Lake 20 18 Snow Water Equivalent (inches) 16 14 12 10 8 6 4 2 0 Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep 2017 Average 22 Snowpack in Bighorn Mountains 20 18 Snow Water Equivalent (inches) 16 14 12 10 8 6 4 2 0 Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep 2017 Average
Based on Most Probable Inflow Forecast (April through July Inflow: 1,864,800 acre-feet) BIGHORN LAKE MONTHLY OPERATIONS Initial Content 773,223 acre-feet Elevation 3611.57 feet Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Total Boysen Release kaf 175.6 184.5 208.1 215.0 107.6 74.4 70.7 59.5 61.5 61.5 55.6 61.5 1335.5 Boysen Release cfs 2951 3001 3497 3497 1750 1250 1150 1000 1000 1000 1001 1000 Buffalo Bill Release kaf 149.5 201.8 238.0 254.5 120.6 103.1 63.0 23.5 21.8 21.8 19.8 21.9 1239.3 Buffalo Bill Release cfs 2512 3282 4000 4139 1961 1733 1025 395 355 355 357 356 Station Gain kaf 75.4 72.5 141.7-51.8-42.8 19.5 68.1 58.3 39.4 44.4 52.0 69.7 546.4 Monthly Inflow kaf 400.5 458.8 587.8 417.7 185.4 197.0 201.8 141.3 122.7 127.7 127.4 153.1 3121.2 Monthly Inflow cfs 6731 7462 9878 6793 3015 3311 3282 2375 1996 2077 2294 2490 Turbine Release kaf 278.5 287.8 278.5 287.8 222.5 191.8 183.2 173.1 179.0 178.9 161.6 179.0 2601.7 Bypass/Spill/Waste kaf 145.8 134.8 133.3 70.9 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 484.8 Total Release kaf 424.3 422.6 411.8 358.7 222.5 191.8 183.2 173.1 179.0 178.9 161.6 179.0 3086.5 Total Release cfs 7131 6873 6921 5834 3619 3223 2979 2909 2911 2910 2910 2911 Spring Flow kaf 4.2 4.3 4.2 4.3 4.3 4.2 4.3 4.2 4.3 4.3 3.9 4.3 50.8 Irrigation Reqmnt kaf 1.8 11.9 22.8 28.1 27.0 17.5 3.0 0.0 0.0 0.0 0.0 0.0 112.1 Afterbay Rels kaf 428.5 426.9 416.0 363.0 226.8 196.0 187.5 177.3 183.3 183.2 165.5 183.3 3137.3 Afterbay Rels cfs 7201 6943 6991 5904 3689 3294 3049 2980 2981 2979 2980 2981 River Release kaf 426.7 415.0 393.2 334.9 199.8 178.5 184.5 177.3 183.3 183.2 165.5 183.3 3025.2 River Release cfs 7171 6749 6608 5447 3249 3000 3001 2980 2981 2979 2980 2981 Min Release kaf 89.3 415.0 89.3 184.5 199.8 178.5 184.5 89.3 92.2 92.2 83.3 92.2 1790.1 End-Month Content kaf 749.4 785.6 961.6 1020.6 983.5 988.7 1007.3 975.5 919.2 868.0 833.8 807.9 End-Month Elevation ft 3607.42 3613.58 3635.00 3640.00 3636.94 3637.38 3638.93 3636.24 3630.84 3624.99 3620.61 3617.00 Net Change Content kaf -23.8 36.2 176.0 59.0-37.1 5.2 18.6-31.8-56.3-51.2-34.2-25.9 34.7 Yellowtail Power Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Total Turbine Release kaf 278.5 287.8 278.5 287.8 222.5 191.8 183.2 173.1 179.0 178.9 161.6 179.0 2601.7 Generation gwh 113.724 117.515 113.724 117.515 90.222 76.585 72.942 67.939 69.771 68.816 60.564 67.616 1036.933 End-Month Power Cap mw 256.6 262.4 282.8 287.5 284.6 285.0 286.5 284.0 278.8 273.3 269.1 265.7 % Max Gen 55 55 55 55 42 37 34 33 33 32 31 32 Ave kwh/af 408 408 408 408 405 399 398 392 390 385 375 378 399 Upstream Generation gwh 25.443 32.524 33.262 35.187 33.043 28.173 23.295 11.570 11.210 11.131 10.005 10.850 265.693 Total Generation gwh 139.167 150.039 146.986 152.702 123.265 104.758 96.237 79.509 80.981 79.947 70.569 78.466 1302.626
Based on Minimum Probable Inflow Forecast (April through July Inflow: 1,108,000 acre-feet) BIGHORN LAKE MONTHLY OPERATIONS Initial Content 773,223 acre-feet Elevation 3611.57 feet Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Total Boysen Release kaf 160.7 123.0 104.2 95.3 76.9 71.4 55.4 47.6 49.2 49.2 44.5 49.2 926.6 Boysen Release cfs 2701 2000 1751 1550 1251 1200 901 800 800 800 801 800 Buffalo Bill Release kaf 143.6 155.6 142.9 151.7 120.7 87.1 59.9 22.2 21.8 21.8 19.8 21.8 968.9 Buffalo Bill Release cfs 2413 2531 2402 2467 1963 1464 974 373 355 355 357 355 Station Gain kaf 27.2 28.3 42.4-66.9-49.8 5.2 52.8 52.2 34.1 38.6 44.7 63.0 271.8 Monthly Inflow kaf 331.5 306.9 289.5 180.1 147.8 163.7 168.1 122.0 105.1 109.6 109.0 134.0 2167.3 Monthly Inflow cfs 5571 4991 4865 2929 2404 2751 2734 2050 1709 1782 1963 2179 Turbine Release kaf 278.5 192.1 167.4 177.5 176.4 162.1 152.4 149.0 154.0 154.0 139.1 154.0 2056.5 Bypass/Spill/Waste kaf 76.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 76.1 Total Release kaf 354.6 192.1 167.4 177.5 176.4 162.1 152.4 149.0 154.0 154.0 139.1 154.0 2132.6 Total Release cfs 5959 3124 2813 2887 2869 2724 2479 2504 2505 2505 2505 2505 Spring Flow kaf 4.2 4.3 4.2 4.3 4.3 4.2 4.3 4.2 4.3 4.3 3.9 4.3 50.8 Irrigation Reqmnt kaf 1.8 11.9 22.8 28.1 27.0 17.5 3.0 0.0 0.0 0.0 0.0 0.0 112.1 Afterbay Rels kaf 358.8 196.4 171.6 181.8 180.7 166.3 156.7 153.2 158.3 158.3 143.0 158.3 2183.4 Afterbay Rels cfs 6030 3194 2884 2957 2939 2795 2548 2575 2575 2575 2575 2575 River Release kaf 357.0 184.5 148.8 153.7 153.7 148.8 153.7 153.2 158.3 158.3 143.0 158.3 2071.3 River Release cfs 6000 3001 2501 2500 2500 2501 2500 2575 2575 2575 2575 2575 Min Release kaf 357.0 184.5 148.8 153.7 153.7 148.8 153.7 89.3 92.2 92.2 83.3 92.2 1749.4 End-Month Content kaf 750.1 864.9 987.0 989.6 961.0 962.6 978.3 951.3 902.4 858.0 827.9 807.9 End-Month Elevation ft 3607.55 3624.61 3637.23 3637.45 3634.94 3635.09 3636.48 3634.04 3629.01 3623.75 3619.82 3617.00 Net Change Content kaf -23.1 114.8 122.1 2.6-28.6 1.6 15.7-27.0-48.9-44.4-30.1-20.0 34.7 Yellowtail Power Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Total Turbine Release kaf 278.5 192.1 167.4 177.5 176.4 162.1 152.4 149.0 154.0 154.0 139.1 154.0 2056.5 Generation gwh 113.724 74.565 65.498 70.119 69.235 62.792 58.588 56.743 58.337 57.649 50.653 56.767 794.670 End-Month Power Cap mw 256.7 272.9 284.9 285.1 282.7 282.9 284.2 281.9 277.1 272.1 268.4 265.7 % Max Gen 55 35 32 33 32 30 27 27 27 27 26 26 Ave kwh/af 408 388 391 395 392 387 384 381 379 374 364 369 386 Upstream Generation gwh 25.458 31.810 30.763 31.744 30.331 25.471 21.106 10.154 10.144 10.087 9.080 9.815 245.963 Total Generation gwh 139.182 106.375 96.261 101.863 99.566 88.263 79.694 66.897 68.481 67.736 59.733 66.582 1040.633
Based on Maximum Probable Inflow Forecast (April through July Inflow: 2,618,000 acre-feet) BIGHORN LAKE MONTHLY OPERATIONS Initial Content 773,223 acre-feet Elevation 3611.57 feet Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Total Boysen Release kaf 223.2 304.4 297.5 258.1 126.1 89.3 92.2 62.5 64.6 64.6 58.3 72.3 1713.1 Boysen Release cfs 3751 4951 5000 4198 2051 1501 1499 1050 1051 1051 1050 1176 Buffalo Bill Release kaf 158.4 263.2 306.5 315.7 120.6 110.0 66.8 34.9 21.8 21.8 19.8 24.3 1463.8 Buffalo Bill Release cfs 2662 4281 5151 5134 1961 1849 1086 587 355 355 357 395 Station Gain kaf 115.0 124.2 256.0-4.2-29.9 35.3 82.9 65.8 46.2 51.2 60.8 78.4 881.7 Monthly Inflow kaf 496.6 691.8 860.0 569.6 216.8 234.6 241.9 163.2 132.6 137.6 138.9 175.0 4058.6 Monthly Inflow cfs 8346 11251 14453 9264 3526 3943 3934 2743 2157 2238 2501 2846 Turbine Release kaf 278.5 287.8 278.5 287.8 253.3 236.4 213.9 188.7 195.0 195.0 176.1 194.9 2785.9 Bypass/Spill/Waste kaf 217.1 376.6 443.8 200.5 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1238.0 Total Release kaf 495.6 664.4 722.3 488.3 253.3 236.4 213.9 188.7 195.0 195.0 176.1 194.9 4023.9 Total Release cfs 8329 10805 12139 7941 4120 3973 3479 3171 3171 3171 3171 3170 Spring Flow kaf 4.2 4.3 4.2 4.3 4.3 4.2 4.3 4.2 4.3 4.3 3.9 4.3 50.8 Irrigation Reqmnt kaf 0.0 11.9 22.8 28.1 27.0 17.5 3.0 0.0 0.0 0.0 0.0 0.0 110.3 Afterbay Rels kaf 499.8 668.7 726.5 492.6 257.6 240.6 218.2 192.9 199.3 199.3 180.0 199.2 4074.7 Afterbay Rels cfs 8399 10875 12209 8011 4189 4043 3549 3242 3241 3241 3241 3240 River Release kaf 499.8 656.8 703.7 464.5 230.6 223.1 215.2 192.9 199.3 199.3 180.0 199.2 3964.4 River Release cfs 8399 10682 11826 7554 3750 3749 3500 3242 3241 3241 3241 3240 Min Release kaf 499.8 92.2 89.3 92.2 230.6 223.1 215.2 89.3 92.2 92.2 83.3 92.2 1891.6 End-Month Content kaf 774.2 801.6 939.3 1020.6 984.1 982.3 1010.3 984.8 922.4 865.0 827.8 807.9 End-Month Elevation ft 3611.73 3616.06 3632.89 3640.00 3636.99 3636.83 3639.17 3637.05 3631.18 3624.62 3619.80 3617.00 Net Change Content kaf 1.0 27.4 137.7 81.3-36.5-1.8 28.0-25.5-62.4-57.4-37.2-19.9 34.7 Yellowtail Power Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Total Turbine Release kaf 278.5 287.8 278.5 287.8 253.3 236.4 213.9 188.7 195.0 195.0 176.1 194.9 2785.9 Generation gwh 113.724 117.515 113.724 117.515 103.613 96.291 86.838 75.129 76.964 75.838 66.786 74.487 1118.424 End-Month Power Cap mw 260.7 264.8 280.8 287.5 284.7 284.5 286.7 284.7 279.1 272.9 268.3 265.7 % Max Gen 55 55 55 55 48 46 41 36 36 35 35 35 Ave kwh/af 408 408 408 408 409 407 406 398 395 389 379 382 401 Upstream Generation gwh 25.239 31.732 33.136 35.159 34.715 30.514 26.248 15.053 11.456 11.376 10.234 12.400 277.262 Total Generation gwh 138.963 149.247 146.860 152.674 138.328 126.805 113.086 90.182 88.420 87.214 77.020 86.887 1395.686
BIGHORN LAKE BIGHORN LAKE ELEVATION 3645 3640 Top of Joint-Use Conservation - Elevation 3640 (1,020.6 kaf) 1088.1 1020.6 3635 961.6 3630 911.3 Elevation (feet) 3625 3620 3615 3610 3605 3600 3595 NPS Recommended Minimum Lake Level Horseshoe Bend Minimum Boat Launch Elevation 868.1 829.2 794.6 764.0 736.2 709.9 684.2 659.3 Storage (KAF) 3590 635.1 3585 3580 Ok-A-Beh & Barry's Landing Minimum Boat Launch Elevation 611.6 588.8 3575 566.5 4/1/18 5/1/18 6/1/18 7/1/18 8/1/18 9/1/18 10/1/18 11/1/18 12/1/18 1/1/19 2/1/19 3/1/19 4/1/19 Maximum Probable Most Probable Minimum Probable 12,000 BIGHORN RIVER FLOW BELOW AFTERBAY 10,000 8,000 Flow (cfs) 6,000 Approximate Powerplant Capacity = 6,150 cfs 4,000 2,000 0 Apr May Jun Jul Aug Sep Oct Nov Dec Jan 2019 Maximum Probable Most Probable Minimum Probable Feb 2019 Mar 2019